disk_integrity.c

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <assert.h>
#include <string.h>
#include <fcntl.h>


#define MB 1000 * 1000
#define GB 1000 * MB
#define FNAME "test.data"


int write_data(char *fname, char *data) {
    // Open file
    int fd = open(fname, O_RDWR|O_CREAT|O_TRUNC, 0660);
    assert(fd != -1);

    int total_bytes = 0;
    while (total_bytes < GB) {
        // Write 1 MB of data to the file
        int bytes = write(fd, data, MB);
        total_bytes += bytes;
        assert(bytes == MB);
    }
    close(fd);

    // Make sure that we have written 1GB of data
    assert(total_bytes == GB);
    return total_bytes;
}

int verify_data(char *fname, char *data) {
    // Allocate a buffer to store data read from file
    char *buffer = malloc(MB);
    assert(buffer != NULL);

    // Open file
    int fd = open(fname, O_RDONLY);
    assert(fd != -1);

    int total_bytes = 0;
    while (total_bytes < GB) {
        // Read 1 MB of data from the file
        int bytes = read(fd, buffer, MB);
        total_bytes += bytes;
        assert(bytes == MB);

        // Verify the data -- buffer and data should contain the same data
        assert(memcmp(buffer, data, MB) == 0);

        // Reset the buffer by overwriting with null characters
        memset(buffer, '\0', MB);
    }
    close(fd);
    free(buffer);

    // Make sure that we have read 1GB of data
    assert(total_bytes == GB);
    return total_bytes;
}

int main(int argc, char *argv[]) {
    // Allocate 1MB of data on the heap and fill it with a's
    // This is our test data which will be written to disk
    char *data = malloc(MB);
    assert(data != NULL);
    memset(data, 'a', MB);

    int count = 0;

    while (1) {
        char fname[128];
        sprintf(fname, "%s.%05d", FNAME, count++);

        // Write 1 GB of data to a file
        // The data is written in chunks of 1MB at the time
        int bytes_written = write_data(fname, data);

        // Read 1GB of data from the same file and verify that the data hasnt changed
        // The data is read in chunks of 1MB at the time
        int bytes_read = verify_data(fname, data);

        printf("Wrote %d bytes and verified %d bytes, no errors found!\n", bytes_written, bytes_read);
    }
    return 0;
}